let obj = {
    a: 1,
    b: 2,
    c: 3
  }
  
  let proxy = new Proxy(obj, {
    get: function(target, key) {
      return target[key]
    },
    set: function(target, key, value) {
      target[key] = value
    },
    // xxxx 11个函数
  })
  
  proxy.a = 10
  console.log(proxy.a);
  